Method and apparatus for use of porous implants

ABSTRACT

An orthopedic prosthesis for implantation into a bone of a patient includes a porous metal shell adapted to be affixed within the bone. The porous metal shell includes an outer surface adapted to receive bone ingrowth and an inner surface adapted to engage a liner. The porous metal shell is porous from the outer surface to the inner surface. A non-porous member may be affixed to the porous metal shell. The non-porous member may include a piercing member extending from the outer surface, the piercing member adapted to penetrate the bone in an implanted position. The non-porous member may include spikes or fins. In one example, the piercing member may define a reduced material cross section at an interface with the outer surface of the porous metal shell. The piercing member may be adapted to be broken at the reduced material cross section and removed from the porous metal shell.

This application is a continuation of U.S. patent application Ser. No. 11/357,868, filed Feb. 17, 2006, now U.S. Pat. No. 7,597,715 B2, which is a continuation-in-part of U.S. patent application Ser. No. 11/294,692, filed Dec. 5, 2005, which is a continuation-in-part of U.S. patent application Ser. No. 11/111,123, filed Apr. 21, 2005 now abandoned. The disclosures of the above applications are incorporated herein by reference.

FIELD

The present invention relates to porous implants and more particularly to porous implants for promoting bone growth used in load bearing applications, anchoring or as augments for replacing removed portions of bone.

INTRODUCTION

Porous coated implants have been used to promote biologic fixation of surrounding bony tissue. In one example, porous material may be coated on an exterior surface of a prosthetic implant to encourage ingrowth of surrounding bone into the pore spaces of the porous material. Typically, the porous coating may comprise stainless steel, titanium, titanium alloys, tantalum, cobalt-chromium alloys, ceramics, polymers and other materials that are suited for use in a biocompatible environment. Various joining methods have been employed to attach the porous coating to a desired prosthetic implant. For example, soldering, brazing, adhesive joining, laser welding, diffusion bonding, metallurgic bonds and mechanical joining have been shown to suitably attach the porous material to a desired implant.

SUMMARY OF THE INVENTION

An orthopedic prosthesis for implantation into a bone of a patient includes a porous metal shell adapted to be affixed within the bone. The porous metal shell includes an outer surface adapted to receive bone ingrowth after the implantation and an inner surface adapted to engage a liner. The porous metal shell is porous from the outer surface to the inner surface. The porous metal shell has a first portion that has a first porosity and a second portion that has a second, distinct porosity.

According to various features, the porous metal shell has a rim portion that has a reduced porosity as compared to a remainder of the porous metal shell. The porous metal shell can have a reduced porosity at the inner surface as compared to the outer surface. The porous metal shell can include a hemispherical body that includes the rim. The hemispherical body can have an apex, wherein the second portion is provided adjacent to the apex.

An orthopedic prosthesis for implantation into a bone of a patient includes an integrally formed shell having an outer portion comprising a first porous layer adapted to receive bone ingrowth after implantation. An inner portion includes a second porous layer and an intermediate portion includes a solid membrane. A fixation member may be adapted to be interoperatively inserted through the shell from the inner portion to the outer portion and pierce the solid membrane. The solid membrane may be adapted to inhibit particles from migrating from the inner portion to the outer portion.

According to various features, a bearing liner may be affixed to the inner portion. The integrally formed shell may define a hemispherical section wherein the fixation member may be adapted to be received at any desired location around the hemispherical section. According to other features, the first and second porous layer may define preformed passages adapted to accept a fastener therethrough.

An orthopedic prosthesis for implantation into a bone of a patient includes an integrally formed shell having an outer portion, an inner portion and an intermediate portion. The outer portion comprises porous metal adapted to receive bone ingrowth after implantation. The inner portion comprises ceramic and defines a bearing surface. The intermediate portion comprises a transition layer. The transition layer may comprise at least one of powdered metal and ceramic. According to other features, the intermediate layer may encapsulate the inner portion.

Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiments of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:

FIG. 1 is a perspective view of a porous metal cup incorporating solid features according to the present teachings;

FIG. 1A is a detail view of an exemplary solid plug defining an apical hole of the porous metal cup of FIG. 1;

FIG. 2 is an assembly sequence illustrating an exemplary method of affixing the solid features of FIG. 1 to the porous metal cup;

FIGS. 3-6 are perspective views of porous metal cups incorporating solid features according to additional features;

FIG. 7 is a perspective view of an exemplary porous metal augment according to the present teachings; FIGS. 7A and 7B are perspective views of an exemplary porous metal augment according to additional features;

FIGS. 8 and 9 are perspective views of the exemplary porous metal augment of FIG. 7 shown cooperating with an exemplary porous metal shell;

FIG. 10 is a perspective view of a porous metal shell incorporating a solid metal rim according to additional features;

FIG. 11 is a sectional view of the porous metal shell of FIG. 10 taken along line 11-11;

FIG. 12 is a side view of an exemplary assembly step wherein the solid metal rim is placed around a dome;

FIG. 13 is an exemplary assembly step wherein a porous metal concentration is arranged in a cold isostatic press with the solid metal rim;

FIG. 14 illustrates an exemplary assembly step wherein the porous metal shell and solid rim are placed within a furnace;

FIG. 15 illustrates an assembly tool according to the present teachings adapted to mate with the solid metal rim during implantation;

FIG. 16 illustrates the assembly tool of FIG. 15 shown mated with the solid metal rim;

FIG. 17 is an exploded view of the assembly tool of FIG. 15 shown with the porous metal cup;

FIG. 18 is a perspective view of the assembly tool of FIG. 15 cooperating with an exemplary impaction handle;

FIG. 19 is a sectional view of FIG. 18 taken along line 19-19;

FIG. 20 is a cutaway view of a porous metal cup according to additional features;

FIG. 21 is a cutaway view of a porous metal cup having a solid metal intermediate layer according to additional features;

FIG. 22 is a cutaway view of the porous metal cup of FIG. 21 shown with predefined passages according to additional features;

FIG. 23 is a partial perspective view of the porous metal cup of FIG. 21 shown in an implanted position;

FIG. 24 is a sectional view of an exemplary porous metal cup according to additional features;

FIG. 25 is a sectional view of an exemplary porous metal cup according to additional features;

FIG. 26 is a perspective view of an exemplary porous metal cup according to additional features;

FIG. 27 illustrates an assembly tool according to the present teachings adapted to mate with the solid metal rim during implantation;

FIG. 28 illustrates the assembly tool of FIG. 27 shown mated with the solid metal rim;

FIG. 29 is an exploded view of the assembly tool of FIG. 27 shown with the porous metal cup;

FIG. 30 is a perspective view of the assembly tool of FIG. 27 cooperating with an exemplary impaction handle;

FIG. 31 is a sectional view of FIG. 30 taken along line 31-31;

FIG. 32 illustrates an assembly tool according to the present teachings adapted to mate with the solid metal rim during implantation;

FIG. 33 illustrates the assembly tool of FIG. 32 shown mated with the solid metal rim;

FIG. 34 is an exploded view of the assembly tool of FIG. 32 shown with the porous metal cup;

FIG. 35 is a perspective view of the assembly tool of FIG. 32 cooperating with an exemplary impaction handle;

FIG. 36 is a sectional view of FIG. 35 taken along line 36-36;

FIG. 37 illustrates an assembly tool according to the present teachings adapted to mate with the solid metal rim during implantation;

FIG. 38 illustrates the assembly tool of FIG. 37 shown mated with the solid metal rim;

FIG. 39 is an exploded view of the assembly tool of FIG. 37 shown with the porous metal cup;

FIG. 40 is a perspective view of the assembly tool of FIG. 37 cooperating with an exemplary impaction handle; and

FIG. 41 is a sectional view of FIG. 40 taken along line 41-41;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of the embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. Furthermore, while the present teachings are described in association with an acetabular cup for a hip joint, those skilled in the art will appreciate that the present teachings may be incorporated into various orthopedic implants for a human body such as knee, shoulder, and other joints. Therefore, it is to be understood that the present illustrative embodiments are not meant to limit the present invention.

With reference to FIGS. 1-6, a series of acetabular cups constructed in accordance to the present teachings are shown and generally identified at reference numerals 10 a-10 e. The acetabular cups 10 a-10 e generally define a shell 12 a-12 e having an inner surface 14 a-14 e and an outer surface 16 a-16 e. A plurality of solid features 20 a-20 e are arranged around the outer surface 16 a-16 d of the shell 10 a-10 d (FIGS. 1-5), or within the shell 10 e (FIG. 6). In one example, the shells 12 a-12 e may be formed entirely of porous metal 22 extending from the inner surface 14 a-14 d to the outer surface 16 a-16 d. The porous metal 22 may comprise stainless steel, titanium, titanium alloys, cobalt-chromium alloys and other materials that are suited for use in a biocompatible environment. The solid features 20 a-20 e may be formed of non-porous material such as stainless steel, titanium, titanium alloys, cobalt-chromium alloys and other materials that are suited for use in a biocompatible environment. The outer surface 16 a-16 e may be adapted to receive bone ingrowth after implantation. According to some embodiments (FIGS. 1-3), the solid features 20 a-20 b extending from the outer surface 16 a-16 b are adapted to penetrate bone in an implanted position. As will be described in greater detail, the solid features 20 a-20 d may be molded into the porous metal cup 10 a-10 d or added in a subsequent joining step.

With specific reference to FIG. 1, the solid features 20 a may comprise a plurality of piercing members or spikes 28. The spikes 28 may be molded into the porous metal cup 10 a as shown in FIG. 1, or alternatively, affixed to the porous metal cup 10 a in a subsequent joining step as shown in FIG. 2. In one example, apertures 30 may be formed such as by a drill bit 32. A proximal shank 34 of the spike 28 may then be inserted through the apertures 30 and secured such as by adhesive or welding. In one example, some or all of the spikes may have a reduced material thickness at an interface with an outer surface of the porous metal cup 10 a (see shank 29 provided on spike 28′). As such, some or all of these spikes may be broken away from the porous metal cup 10 a such as by hand or with an impacting tool. A solid plug 36 (FIG. 1A) defining an apical hole may be threaded for mating with a cup insertion instrument. While the solid plug 36 is specifically shown on the porous metal cup 10 a, the solid plug 36 may be provided on any acetabular cup disclosed herein.

With reference to FIG. 3, the porous metal cup 10 b having inner surface 14 b and outer surface 16 b is shown. The plurality of solid features 20 b may comprise fins 38 molded into the porous metal cup 10 b. The fins 38 may be arranged around the outer surface 16 b of the shell 12 b. The fins 38 generally define a planar section 40 extending outwardly from the outer surface 16 b of the shell 12 b. While not specifically shown, the fins 38 may alternatively be affixed to the porous metal cup 10 b in a subsequent joining step as described with respect to porous metal cup 10 a (FIG. 2). In one example, some of the fins 38 may be broken away from the outer surface 16 b of the shell 12 b interoperatively. Similar to the break away spikes 28′ described above, some or all of the fins may have a reduced material thickness at an interface with an outer surface of the porous metal cup 10 a (see finger 39 provided on fin 38′). As such, some or all of these fins may be broken away from the porous metal cup 10 a such as by hand or with an impacting tool.

As illustrated in FIG. 4, the solid features 20 c may include cannulated cylinders 42 adapted to be received in bores 44 defined through the shell 12 c. Again, the solid features 20 c may be molded with the porous metal shell 12 c or alternatively, added subsequent to formation of the porous metal shell 12 c. In this way, the plurality of bores 44 may be defined during a molding step of the porous metal shell 12 c or formed through a machining operation such as drilling (see e.g. FIG. 2). The cannulated cylinders 42 may be affixed to the shell 12 c by any suitable method such as adhesive or welding. In one example, the cannulated cylinders may be adapted to receive fasteners such as bone screws through bores 44 during implantation. In one example, an inner diameter 45 of a bore 44′ and an outer diameter 46 of a cannulated cylinder 42′ can be tapered to facilitate a compression fit.

FIG. 5 illustrates the porous metal cup 12 d having inner surface 14 d and outer surface 16 d. The plurality of solid features 20 d may comprise grommets 48. In one example, the grommets 48 may be used interoperatively to form a barrier at unused bores 44 in the shell 12 d. In one example, an inner diameter 45 of a bore 44′ and an outer diameter 49 of a grommet 48′ can be tapered to facilitate a compression fit.

FIG. 6 illustrates a hemispherical webbing 50 integrally formed during a molding step with the porous metal shell 12 e. The hemispherical webbing 50 may comprise a non-porous biocompatible metal such as titanium. The hemispherical webbing 50 may be adapted to provide structural support to the porous metal shell 12 e.

With reference to FIG. 7, an augment 52 is shown. The augment 52 may be formed of porous metal such as by one of the materials disclosed herein. A series of solid features 20 such as bone spikes or screws 58 are shown extending from the augment 52. In one example, the bone screws 58 may be inserted interoperatively through a series of bores 60 (FIG. 7) provided through the augment 52. A series of augments having various sizes and/or porosity may be provided. FIGS. 8 and 9 illustrate the augment 52 adjacent an acetabular cup 10 f. The acetabular cup 10 f may be formed of porous metal such as described herein. A series of apertures 64 may be formed on the acetabular cup 10 f for receiving fasteners (not specifically shown) during implantation. The configuration and orientation of the apertures 64 are merely exemplary. It is appreciated that the augments shown may alternatively be used with other acetabular cups such as those disclosed herein. As shown, an outer radial wall 70 (FIG. 7) of the augment 52 cooperates with an outer radial wall 72 of the cup 10 f in a side by side relationship. In one example poly methyl methacrylate (PMMA) bone cement 74 may be used to join the augment 52 to the acetabular cup 10 f. Other joining techniques may also be used such as mechanical fastening. The augment 52 may be used to fill an area adjacent the acetabular cup 10 f such as where a bone defect was removed.

An exemplary method of making the acetabular cups 10 a-10 f according to the present teachings will now be described. In one example, a mixture of metallic powder, such as titanium powder or cobalt-chromium alloy powder, and a binder, such as ammonium bicarbonate or d-limonene may be combined together into a homogeneous mixture. In one example, the metallic powder and binder may be placed into a containment device such as a bag and sealed. The bags may then be placed into a cold isostatic press (CIP) defining an inverse acetabular shell and pressure applied. The CIP shapes the mixture into an acetabular shell. The solid features 12 a-12 e may be molded into the porous metal concurrently with the CIP, or alternatively be added after such as by a machining operation. The acetabular cup 10 a-10 f may then be placed into a furnace and baked for a predetermined timeframe suitable to burn off the binder. One exemplary cycle includes 400 degrees C. for 12 hours. If necessary, a subsequent machining step may be performed on the solid features 12 a-12 e. Other exemplary methods for making porous acetabular cups may be found in co-pending application, U.S. patent application Ser. No. 11/357,929, filed Feb. 17, 2006, entitled “Method and Apparatus for Forming Porous Metal Implants”, also assigned to Biomet Manufacturing Corp., of Warsaw Ind., which is incorporated herein by reference.

Turning now to FIGS. 10 and 11 an acetabular cup 10 g having a porous metal shell 12 g and an integrally molded solid feature 20 g in the form of a solid ring or rim 80 is shown. The solid ring 80 may be formed of biocompatible metal such as, but not limited to, solid titanium or titanium alloy. An outer face 82 of the solid ring 80 defines an attachment feature 84 in the form of raised walls 86 extending from a planar surface 88. The raised walls 86 each define a first tapered surface 90 (FIG. 11). As will be described, the raised walls 86 mate with complementary structure provided on an attachment tool during implantation.

With specific reference to FIG. 11, an interface surface 92 between the porous metal shell 12 g and the solid ring 80 is shown. A metallurgical bond is created at the interface surface 92 during formation of the acetabular cup 10 g as will be described in greater detail. A first annular pocket 96 is defined around an inner radius of the porous metal shell 12 g. Similarly, a second annular pocket 98 is defined around an outer radius of the solid ring 80. A first collar 102 formed on the solid ring 80 nests in the first annular pocket 96 of the porous metal shell 12 g. A second collar 106 formed on the porous metal shell 12 g nests in the second annular pocket 98 of the solid ring 80. The respective pockets 96 and 98 and collars 102 and 106 provide an overhanging interlock between the porous metal shell 12 g and the solid ring 80 for increased structural integrity. As illustrated in FIG. 11, a liner 100 is shown captured within the porous metal shell 12 g by an annular ring 101.

With reference to FIGS. 12-14, an exemplary method of making the acetabular cup 10 g according to the present teachings will now be described. In one example, a blank of solid metal may be initially machined into the solid metal ring 80. Next, the machined ring 80 may be located over a dome 110 (FIG. 12). A mixture of metallic powder and binder 112 is then prepared into a homogeneous mixture as described above. The mixture of metallic powder and binder 112 may be placed into a containment member such as a bag (not specifically shown) and located over the dome 110 and solid metal ring 80 in a CIP 118. The CIP 118 applies high pressure onto the mixture 112 and solid metal ring 80 to form a metallurgical bond at the interface surface 92. The porous metal shell 12 g and solid metal ring 80 assembly are then removed from the CIP 118. The porous metal shell 12 g may present a hard, wet sandy consistency. The porous metal 12 g shell may then be machined to create a uniform thickness around its semi-hemisphere. Passages 120 (FIG. 10) may also be machined. It is contemplated that the passages 120 may be alternatively formed by extensions located on the dome 110 during the CIP process. It is appreciated that a combination of some or all of the other solid features may be molded to the porous metal shell.

The assembly (porous metal shell 12 g and solid ring 80) may then be placed into a furnace 122 and baked for a predetermined timeframe suitable to burn off the binder. An exemplary cycle includes 400 degrees C. for 12 hours. The solid 80 ring may be subsequently machined if necessary to define the desired shape. The augment 52 may be formed utilizing similar steps as described above.

With reference now to FIGS. 15-19, an exemplary implantation tool 130 (FIG. 18) will be described. The implantation tool 130 generally includes a handle 132, a housing 134, a T-bar 136 (FIG. 17) and a plate 138. The housing 134 can include a cup portion 140 having a pair of passages 142 defined through a radial wall (FIG. 17). The housing 134 can define a pair of raised wall portions 146 and a pair of recessed wall portions 148 (FIG. 15). The T-bar 136 can include a longitudinal portion 152 (FIG. 17) having fingers 154 extending on opposite ends. A shaft portion 160 extends centrally from the longitudinal portion 152 in a direction opposite the fingers 154. The shaft portion 160 is adapted to cooperate with a driver as will be described in greater detail later. The fingers 154 nest in the passages 142 of the housing 134. The T-bar 136 is operable to move axially relative to the housing 134 along the passages 142 to facilitate a gripping action onto the solid ring 80. More specifically, the fingers 154 of the T-bar 136 each define second tapered surfaces 162 (FIG. 17) adapted to mate with the first tapered surfaces 90 of the raised walls 86 on the solid ring 80 (FIG. 19). Once the respective tapered surfaces 90, 162 engage, the T-bar 136 may be translated axially away from the acetabular cup 10 g thereby creating tension between the respective tapered surfaces 90, 162. The plate 138 may be adapted to locate within an annular space defined by the cup portion 140.

With specific reference to FIGS. 18 and 19, the handle 132 will now be described in greater detail. The handle 132 generally includes a gripping member 168 disposed along a longitudinal shaft portion 166 and a knob 170 having an impacting surface. Rotation of the knob 170 communicates axial movement to the T-bar 136 through a locking interface 172. While not specifically, shown, a core may be housed within the tool (near the knob 170) and threadably connected to the knob 170. A cable may connect the core with the locking interface 172. In this way, rotation of the knob results in axial movement of the T-bar 136. The locking interface 172 may comprise a quick connect or other suitable connection.

An exemplary method of using the implantation tool 130 will now be described. At the outset, the raised walls 146 of the cup portion 140 are aligned with the planar surface 88 of the solid ring 80. Next, the cup portion 140 and the T-bar 136 are rotated by way of the handle 132, such that the second tapered surfaces 162 of the fingers 154 slidably locate under the first tapered surfaces 90 of the raised walls 86 on the solid ring 80. In one example, the cup portion 140 and the T-bar 136 are rotated about 20 degrees clockwise to achieve an interlocking relationship. Next, the gripping member 168 is translated upward as viewed in FIG. 18 to create tension between the first and second tapered surfaces 90, 162 as described above. Once the installation tool 130 has securely retained the acetabular cup 10 g, the acetabular cup 10 g may be located into a desired location on the patient (not shown). The impacting surface of the knob 170 may then be struck with an impacting tool until the acetabular cup 10 g has been implanted. Once the acetabular cup 10 g has been implanted to a desired position, the handle 132 may be rotated in an opposite direction until the tapered surfaces 162 of the fingers 154 are disengaged with the tapered surfaces 90 of the raised walls 86 on the solid ring 80. The implantation tool 130 may then be removed.

It is appreciated that the acetabular cup 10 g may be secured to the implantation site by any suitable methods such as fasteners through passages 120 and/or bone cement. Inserts 176 (FIG. 17) may optionally be placed through the passages 120 or molded therein.

Turning now to FIG. 20, an acetabular cup 10 h according to additional features will be described. The acetabular cup 10 h generally includes a porous metal outer layer 200, a pressed metal powder intermediate layer 202, and a solid ceramic inner layer 204. An exemplary method of making the acetabular shell 10 h includes forming a solid ceramic insert 204 having a rough, or textured outer surface 210. Powdered metal may then be pressed onto the textured outer surface 210 of the ceramic insert 204. The pressed powdered metal 202 may define a thin cross-section relative to the inner ceramic layer 204 and the outer porous metal layer 200. The powdered metal 202 may comprise biocompatible metals such as those disclosed herein. A porous metal layer 200 may then be formed on an outer surface 212 of the pressed powdered metal 202. The porous metal layer 200 may comprise biocompatible metal such as those described herein. The porous metal layer 200 may be formed onto the pressed powdered metal layer 202 by any suitable method such as by CIP, as disclosed herein. The assembly may then be placed into a furnace and sintered. The resulting acetabular cup 10 h is one-piece having a ceramic bearing surface 216 and a porous metal outer surface 218. The porous metal outer surface 218 facilitates bone ingrowth.

With reference now to FIGS. 21-23, acetabular cups 10 i and 10 j constructed in accordance to additional features will be described. The acetabular cup 10 i generally includes an outer porous metal layer 220, an inner porous metal layer 222 and a thin solid metal intermediate layer 224. In one example, the intermediate layer 224 may define an annular rim 228 around the outer porous metal layer 220. Again, the outer porous metal layer 220 is adapted to facilitate bone ingrowth. The inner porous layer 222 may be adapted to accept adhesive such as bone cement for cementing a liner. The inner porous layer 222 may be additionally or alternatively integrally molded with a polyethylene material.

The thin solid metal intermediate layer 224 is adapted to act as a barrier to inhibit migration of wear debris particles through the cup 10 i and onto a bone-implant interface. In addition, the thin solid metal intermediate layer 224 may be pierced by a tool, such as a drill bit or fastener, such as a bone screw, intra-operatively for fixation at the implantation site. Because the intermediate layer 224 is uniform around the semi-hemisphere of the acetabular cup 10 i, a surgeon is not limited to predefined, fixed locations for passing a fastener during implantation. Explained more clearly, the uniform intermediate layer 224 allows a surgeon to pass a fastener at any location around the semi-hemisphere of the acetabular cup 10 i. In one example, screw holes (not shown) may be drilled intra-operatively through the acetabular cup 10 i (FIG. 21). A surgeon may drill screw holes at locations that provide optimal fixation in the host bone without concern that wear particles will migrate onto the bone interface. In one example, the intermediate layer 224 defines a thickness less than 50%, or less than 25% of a thickness of the outer porous metal layer 220 and the inner porous metal layer 222, respectively.

In another example, screw holes 232 shown on acetabular cup 10 j may be pre-defined through the inner and outer porous metal layers 220, 222 (FIG. 22), but closed at the solid intermediate layer 224. In this example, a surgeon may utilize some, or all of the pre-defined holes to pass bone screws through the solid intermediate layer. FIG. 23, illustrates the acetabular cup 10 i in an implanted position secured with fasteners 236 pierced through the intermediate layer 224. While the solid intermediate layer 224 is specifically illustrated in the drawings as between the inner porous layer 222 and outer porous layer 220, the solid intermediate layer 224 may alternatively be formed on an inner concave surface of the cup 10 i. In this way, the solid layer may provide a smooth surface for the bearing to ride.

Turning now to FIGS. 24 and 25, acetabular cups 10 k and 10 m according to additional features are shown. Acetabular cups 10 k and 10 m are each formed of a porous metal shell 12 k and 12 m such as described herein. As illustrated, the porosity is less porous (or more dense) at a rim 240 of the acetabular cup 10 k. In this way, the rim 240 may provide additional strength during implantation. In another example, the acetabular cup 10 k is less porous (or more dense) at an inner surface 14 m of the cup 10 m. As a result, the acetabular cup 10 m may provide additional strength at an interface with a bearing (not shown).

As illustrated in FIG. 26, another exemplary acetabular cup 10 n is shown. The acetabular cup 10 n generally includes a porous metal portion 242 and a solid metal portion 244. The porous metal portion 242 generally is formed on an outer surface 16 n of the acetabular cup 10 n while the solid metal portion 244 is formed on an inner surface 14 n. The solid metal portion 244 defines a pair of annular lips 248 adapted to provide a secure mechanical interface with the porous metal portion 242. Alternatively, a single or a plurality of annular lips 248 may be formed on the solid metal portion 244. The porous metal and solid metal portions 242 and 244, respectively, may comprise biocompatible metal such as those disclosed herein. While not specifically shown, the solid metal portion 244 may include raised walls having tapered surfaces for mating with an installation tool such as disclosed herein.

With reference now to FIGS. 27-31, another exemplary implantation tool 250 (FIG. 30) will be described. The implantation tool 250 generally includes the handle 132, a housing 256, a central member 260, a plate 261 and a pair of fingers 262. The housing 256 can include a cup portion 268 having a pair of passages 270 defined through a radial wall. A shaft portion 272 extends centrally from the central member 260 in a direction opposite the fingers 262. Pins 274 locate within respective bores 276 of the central member 260 and slots 278 of the fingers 262. The shaft portion 272 is adapted to cooperate with a driver such as disclosed above in relation to implantation tool 130. The fingers 262 nest in the passages 270 of the housing 256. The plate 261 may be adapted to locate within an annular space defined by the cup portion 268. The central member 260 is operable to move axially relative to the housing 256 along the passages 270 to facilitate a gripping action onto the solid ring 80. More specifically, the fingers 262 each define second tapered surfaces 280 (FIG. 29) adapted to mate with the first tapered surfaces 90 of the raised walls 86 on the solid ring 80 (FIG. 31).

An exemplary method of using the implantation tool 250 will now be described. At the outset, fingers 262 are aligned with the first tapered surfaces 90 of the raised walls 86 on the solid ring 80. Next, the knob 170 is rotated as viewed in FIG. 30 to pivot the fingers 262 outwardly about pins 274 to create tension between the first and second tapered surfaces 90, 280. Once the installation tool 250 has securely retained the acetabular cup 10 g, the acetabular cup 10 g may be located into a desired location on the patient (not shown). The impacting surface of the knob 170 may then be struck with an impacting tool until the acetabular cup 10 g may be secured to the implantation site by any suitable methods. Once the acetabular cup 10 g has been implanted to the desired position, the knob 170 may be rotated in an opposite direction to pivot the fingers 262 inwardly and away from engagement with the tapered surfaces 90. The implantation tool 250 may then be removed.

With reference now to FIGS. 32-35, another exemplary implantation tool 300 (FIG. 30) will be described. The implantation tool 300 generally includes the handle 132, a housing 302, a central member 304 and a pair of fingers 310. The housing 302 can include a cup portion 312 having a pair of passages 314 defined through a radial wall. A shaft portion (not show) extends centrally from the central member 304 in a direction opposite the fingers 310. Pins 318 locate within respective bores 220 of the central member 304 and 322 of the fingers 310. Similarly, pins 326 locate within respective bores 228 of the central member 304 and 330 of the housing 302. The shaft portion is adapted to cooperate with a driver such as disclosed above in relation to implantation tool 130. The fingers 310 nest in the passages 314 of the housing 302. The central member 304 is operable to move axially relative to the housing 302 along the passages 314 to facilitate a gripping action onto the solid ring 80. More specifically, the fingers 310 each define second tapered surfaces 332 (FIG. 34) adapted to mate with the first tapered surfaces 90 of the raised walls 86 on the solid ring 80 (FIG. 36).

An exemplary method of using the implantation tool 300 will now be described. At the outset, fingers 310 are aligned with the first tapered surfaces 90 of the raised walls 86 on the solid ring 80. Next, the knob 170 is rotated as viewed in FIG. 35 to pivot the fingers 310 outwardly about pins 322 to create tension between the first and second tapered surfaces 90, 332. Once the installation tool 300 has securely retained the acetabular cup 10 g, the acetabular cup 10 g may be located into a desired location on the patient (not shown). The impacting surface of the knob 170 may then be struck with an impacting tool until the acetabular cup 10 g may be secured to the implantation site by any suitable methods. Once the acetabular cup 10 g has been implanted to the desired position, the knob 170 may be rotated in an opposite direction to pivot the fingers 310 inwardly and away from engagement with the tapered surfaces 90. The implantation tool 300 may then be removed.

With reference now to FIGS. 37-41, another exemplary implantation tool 400 (FIG. 40) will be described. The implantation tool 400 generally includes the handle 132, a housing 402, a cap 403, a central member 404, a dome 406 (FIG. 39) and three fingers 408. The housing 402 defines three passage 414 defined through a radial wall. A shaft portion 418 extends centrally from the central member 404 in a direction opposite the fingers 408. Pins 420 locate within respective bores 422 of the central member 404 and angled slots 426 of the fingers 408. The shaft portion 418 is adapted to cooperate with a driver such as disclosed above in relation to implantation tool 130. The fingers 408 nest in the passages 414 of the housing 402. A series of fasteners 416 mate with threaded bores 417 in the housing 402 to retain the central member 404 and fingers 408 between the cap 403 and the housing 402.

The central member 404 is operable to move axially relative to the housing 402 along the passages 414 to facilitate a gripping action onto an inner radial tapered lip 430 of cup 10 p. More specifically, the fingers 408 each define tapered surfaces 432 (FIG. 41) adapted to mate with the radial tapered lip 430 of the cup 10 p. As the shaft portion 418 is urged upward (FIGS. 39 and 41), upper surfaces 438 of the fingers 408 slidably ride in a radially outward direction along a lower surface 440 of the cap 403. The pins 420 ride along the angled slots 426 causing the fingers 408 to move radially outwardly during upward movement of the central member 404.

An exemplary method of using the implantation tool 400 will now be described. At the outset, the fingers 408 are aligned with the radial tapered lip 430 of the cup 10 p. Next, the knob 170 is rotated as viewed in FIG. 40 to slide the fingers 408 outwardly to create tension between the tapered surfaces 432 of the fingers 408 with the radial tapered lip 430 of the cup 10 p. Once the installation tool 400 has securely retained the acetabular cup 10 p, the acetabular cup 10 p may be located into a desired location on the patient (not shown). The impacting surface of the knob 170 may then be struck with an impacting tool until the acetabular cup 10 p may be secured to the implantation site by any suitable methods. Once the acetabular cup 10 g has been implanted to the desired position, the knob 170 may be rotated in an opposite direction to pivot the fingers 408 inwardly and away from engagement with the radial tapered lip 430. The implantation tool 400 may then be removed.

While the invention has been described in the specification and illustrated in the drawings with reference to various embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention as defined in the claims. Furthermore, the mixing and matching of features, elements and/or functions between various embodiments is expressly contemplated herein so that one of ordinary skill in the art would appreciate from this disclosure that features, elements and/or functions of one embodiment may be incorporated into another embodiment as appropriate, unless described otherwise above. Moreover, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment illustrated by the drawings and described in the specification as the best mode presently contemplated for carrying out this invention, but that the invention will include any embodiments falling within the foregoing description and the appended claims. 

1. An acetabular cup for implantation into an acetabulum of a patient, the acetabular cup comprising: an integrally formed shell having an outer hemispherical portion comprising a first porous metal layer adapted to receive bone ingrowth after implantation, an inner hemispherical portion comprising a second porous metal layer; and a thin solid metal intermediate hemispherical portion defining a non-porous and continuous barrier between said outer and inner hemispherical portions; at least one bone screw adapted to be intra-operatively inserted through the shell from the inner portion to the outer portion, the at least one bone screw adapted to pierce the barrier; and a bearing liner affixed to the inner portion; wherein the barrier inhibits wear debris particles from migrating from the inner portion to the outer portion; wherein the outer portion defines a radial rim, wherein the intermediate portion includes an annular collar affixed around the radial rim; wherein the intermediate portion has a thickness less than 50% of either of a thickness of the inner portion and a thickness of the outer portion; wherein the porosity of the first porous metal layer is distinct from the porosity of the second porous metal layer.
 2. The acetabular cup of claim 1 wherein the intermediate portion has a thickness less than 25% of either of a thickness of the inner portion and a thickness of the outer portion.
 3. The acetabular cup of claim 1 wherein the inner portion includes integrally molded polyethylene.
 4. The acetabular cup of claim 1 wherein the integrally formed shell defines a hemispherical section and where the fixation member includes at least one bone screw that is adapted to be received at any desired location around the hemispherical section.
 5. The acetabular cup of claim 4, further comprising a series of fixation members arranged around the hemispherical section in an implanted position.
 6. The acetabular cup of claim 1 wherein the first and second porous metal layers both define preformed passages adapted to accept a fastener therethrough. 